Prediction and diagnosis of male animal fertility is a major concern of those skilled in the art. In humans, about half of the fertility problems arise due to male factors. In addition, 50% of breeding system failures that are contributed by sires (e.g., breeding cattle, breeding horses, breeding pigs, etc.) lead to huge economic drawbacks in the animal industry (Sharlip I D et al., Fertility Steril, 77(5):873-882, 2002). Therefore, the development of new methods is needed to ensure more accurate prediction and diagnosis of male fertility.
Worldwide, artificial insemination (AI) has been extensively performed in animal industries. Recent data revealed that more than 90% of the sows in Europe and the USA have been bred using AI during last three decades (Gerrits R J et al., Theriogenology, 63(2):283-299, 2005). Moreover, AI has been implemented extensively in swine industries for genetic up-gradation (Gadea J, Theriogenology, 63(2):431-444, 2005).
However, the selection of high-quality semen still depends on conventional sperm analyses such as the analysis of sperm morphology, motility, and sperm penetration assays (Bonde J P, Lancet, 352(9135):1172-1177, 1998; Budworth P R et al., J Androl, 9(1):41-54, 1998; Oh S A et al., Anim Reprod Sci, 121(1-2):131-138, 2010). Although these tests are commonly used to evaluate the male factor of fertility/infertility, the clinical value is still debated (Lewis S E, Reproduction, 134(1):31-40, 2007; Braundmeier A G, Journal of Dairy Science, 84:1915-1925, 2001).
To overcome the disadvantages of conventional sperm analyses, a new method capable of measuring sperm function and fertility on humans and economically important animal species should be developed. In addition, it is important to note that the optimization of sperm production will be possible when the methods to choose superior sires with greater efficiency become available.
Several recent studies reported that the use of proteomics as an effective tool aids in understanding the molecular biology of sperm. In fact, increased knowledge of the sperm proteome enabled new molecular markers to be identified (Corner J S et al., In The Sperm Cell, pp 49-71, 2006; de Mateo S et al., Proteomics, 7(23):4264-4277, 2007). In this regard, the identification of superior sire-derived protein biomarkers using proteomics tools will open up new horizons in the fields related to the reproduction of animals.
The ejaculated sperm of mammals undergoes physiological changes such as a capacitation procedure while it exists in the female genital tract for a long period of time (Zaneveld L J et al., Human Reproduction, 6:1265-1274, 1991; Fraser L R et al., Journal of Reproduction and Fertility, 96:363-377, 1992; Kirichok Y et al., Nature, 439:737-740, 2006; Visconti P E, PNAS, 106:667-668, 2009, Kwon W S et al., Fertil Steril, 99:354-61, 2013; Kwon W S et al., PLoS One, 8:e54192, 2013). Because sperm can be fertilized with oocytes after it undergoes the capacitation procedure, the difference between before and after the capacitation procedure is very important in view of sperm fertility. However, to date, studies on the difference in protein expression patterns between before and after capacitation have been mainly conducted without considering litter size.
Accordingly, the present inventors have made extensive efforts to develop a novel method for predicting litter size, and as a result, have found that, when a method of predicting litter size based on the difference in the expression level of a protein marker between before and after sperm capacitation, and a method of predicting semen quality and litter size by chlortetracycline staining based on whether sperm was capacitated, are used, the ability of an individual to produce litter can be effectively predicted, thereby completing the present invention.